The present application describes a magnetic disk apparatus and a magnetic disk apparatus control method for storing information onto a recording medium with magnetic head.
The magnetic disk apparatus writes information onto the magnetic medium with the magnetic head. The magnetic head is lifted over the medium by airflow generated by spinning of the medium.
Generally, outputs from the magnetic head increase and the magnetic properties of the magnetic head improve. Recently, the clearance between the magnetic head and the medium has been decreasing on the order of several nanometers to increase recording density.
Current magnetic disk apparatuses have a dynamic flying height (DFH) control system. The DFH control system controls the clearance between the magnetic head and the magnetic medium. The DFH control system controls the clearance by expanding the magnetic head element with a current supplied to a heating circuit embedded in the magnetic head. Refer FIG. 24, [Under normal atmospheric pressure] and [Supplied heating]
While the magnetic properties improve as the clearance between the head and the medium decreases, the occurrence of head crashes may rise due to infinitesimal projections on the medium. In particular, when an atmospheric pressure decreases, a lift generated by the airflow decreases and therefore the occurrence of head crashes with the magnetic medium may increase. When the head crashes occur, data write and read may interfere with each other, or take more time. In a worst-case scenario, the magnetic head or the magnetic medium may be damaged. Refer to FIG. 24, [Under reduced atmospheric pressure].
Thus, such failures may be prevented by sensing a decrease of the atmospheric pressure.
Generally, outputs from the magnetic head increase and automatic gain control (AGC) gain decreases when the flying height of the magnetic head decreases. Owing to this characteristic, changes of the flying height are detected by monitoring the AGC gain.
However, the clearance between the magnetic head element and the magnetic medium does not always decrease, depending on a design of a magnetic head slider or a suspension when the atmospheric pressure decreases. Furthermore, the AGC gain changes depending on a temperature so that the sensing the change of the atmospheric pressure accurately is difficult. In short, the outputs of the magnetic head do not always increase when the atmospheric pressure decreases. Thus, the change in atmospheric pressure may not be detected accurately with AGC gain alone.